1. Field of the Invention
This invention relates to a hollow shaft, and more particularly to a hollow shaft wherein an externally threaded portion is formed on the outer periphery of an opening portion at an end of a main body thereof, and, for example, to a hollow shaft effectively used as a motor shaft.
2. Related Art Statement
In a construction, in which the hollow shaft is rotatably supported by a motor housing, an externally threaded portion is formed on the outer periphery of an opening at an end of a main body of the hollow shaft and a nut is threadably coupled to this externally threaded portion, to thereby clamp a ball and roller bearing.
As described above, when the ball and roller bearing is clamped to an end portion of the shaft by the nut threadably coupled to the externally threaded portion of the shaft, in order to prevent the spontaneous loosening phenomenon of the nut, a washer for a ball and roller bearing (hereinafter referred to as "a washer for a bearing") is used. Namely, engageable grooves are previously cuttingly formed in the axial direction on the outer peripheries of the externally threaded portion and the nut of the shaft, respectively. The ball and roller bearing is coupled onto the shaft, and thereafter, the washer for the bearing is coupled onto the externally threaded portion while a tongue piece of the washer is inserted into the engageable groove of the externally threaded portion. Subsequently, the nut is threadably coupled onto the externally threaded portion, whereby the ball and roller bearing is clamped by the nut, interposing therebetween the washer for the bearing. Subsequently, a tooth of the washer is engaged with the engageable groove of the nut. In this state, the nut is locked against rotating about the shaft via the washer, so that the nut is reliably prevented from being loosened.
However, in the case that the above-described clamping construction is applied to the hollow shaft, when the nut is strongly clamped to the externally threaded portion, stress is concentrated at the engageable groove formed in the externally threaded portion, whereby the engageable groove shrinks inwardly in the radial direction, so that, the externally threaded portion of this hollow shaft is reduced in diameter and the meshing engagement between the nut and the externally threaded portion becomes improper. thereby unabling to obtain the desired clamping force.
An object of the present invention is to provide the hollow shaft capable of preventing the shrinking phenomenon of the externally threaded portion during clamping.